1. Field of the Invention
This invention relates in general to an apparatus for manipulating the transmission of power. In particular, this invention relates to an apparatus for optimized transmission of mechanical or electrical power produced by a power source to a load, with the transmitted power fulfilling the specific mechanical or electrical power requirement within the full operating speed range of the load.
2. Technical Background
Power is a measure to rate the flow of energy, or work done, per unit time. Electrical power has been conveniently available in households, in factories, and, for example, in the overhead power line system of electrified railway for various applications. On the other hand, mechanical power that is provided as raw motive power by prime movers such as internal combustion engines consuming fossil fuel is also convenient. In practical applications, these are the two forms of readily-available power source in modern society.
The term xe2x80x9cpowerxe2x80x9d is used herein as a general term to designate either the mechanical or the electrical form of power. For the discussion of the invention, xe2x80x9cpower transmissionxe2x80x9d thus broadly refers to the transmission of mechanical or electrical power to either mechanical or electrical power. Relevant forms of power concerning the manipulation of power transmission as performed by the apparatus of the invention thus include mechanical and electrical power.
When both mechanical and electrical forms of power are considered, there can be four possible modes of power transmission. In conventional terminology, the transmission of mechanical power to mechanical is generally referred as mechanical power transmission, as is in vehicular drive train applications. The transmission of electrical power to mechanical, when utilizing an electric motor, is referred to as electric motoring. In contrast, the transmission of mechanical power to electrical, when employing an electric generator, is electrical power generation. Electrical-to-electrical power transmission generally involves the regulation of voltage and/or frequency of the electrical power. In the extreme case of zero frequency of the AC electrical power, it becomes the DC electrical power.
The need for power transmission is based on one simple reason. Namely, the sources providing the power, either mechanical or electrical, are frequently operating to generate the power at conditions not directly desirable at the load that is consuming the power. Generally, the characteristic factors of power source and load concerned include, in the mechanical power, torque and speed and, in the electrical power, frequency and voltage. For both forms of power, efficiency is a factor of ever increasing importance. For example, considering the vast number of internal combustion engine-driven vehicles used world-wide, small improvements in vehicle power plant and transmission efficiencies can be translated into the huge conservation of petroleum consumption. In critical applications such as electric vehicle, the bottleneck of storage battery technology turns the efficiency of electric drive system into one of the most important design factors.
An internal combustion engine needs a transmission box to provide the torque-speed regulation in order to meet propulsion demands at the vehicle driving wheels. Conventional vehicle internal combustion engine does not provide stall torque, while every vehicle has to be accelerated from standstill. This means that an internal combustion engine which operates within a limited speed rangexe2x80x94not including stall speedxe2x80x94must drive the load in a full operating speed rangexe2x80x94including the stall speed. The transmission box in an automobile is used to perform this transmission of mechanical power along with the necessary torque/speed regulations. But traditional automobile transmissions built around multiple-speed-geared torque converters suffer drawbacks. They require the use of precision fluid logic valve mechanism to switch the torque converter among the three or more sets of gear train of different gear ratios. The multiple sets of gear trains installed in a typical transmission box, in which only one is functional at any given time, add to the overall weight of the system, and the torque converter operates with poor efficiency at low speeds.
An electric machine operating in the motoring modexe2x80x94commonly known as the electric motorxe2x80x94does provide stall torque, but with poor efficiency. In large-power electric motor drives, poor starting-speed efficiency imposes heat dissipation problem that the drives must reduce their power rating at low operating speeds in order to prevent permanent damages caused by overheating. Though power electronics devices such as PWM (pulse-width modulation) systems do expand operating speed range and improve motor drive efficiencies, they are generally sophisticated and costly to build.
An electric machine operating in the generating mode as an electric generator is also constrained by input mechanical speed ranges. For example, a wind turbine driving an electric generator has a limitation of minimum wind speed. Below that minimum, the generator system is difficult, if not impossible, to generate an AC power that can be acceptable for house or industrial application.
Thus, when considered as machines for the transmission of the mechanical and/or electrical power in the generalized sense, conventional drive systems, either vehicle transmissions, electric motor drives or generators, all suffer from the low-efficiency performance characteristics at low operating speeds. Yet low-speed operation is a situation inevitable for practically all such power drives. In some situations such as vehicle transmissions operating in traffic congestion conditions, this poor-efficiency performance at low speeds deteriorates air pollution problem at a large scale considering the number of vehicles caught in the traffic. Most of these conventional power transmission machines, though optimized for a fraction, frequently at the high-speed end, of their respective full operating speed range, can not cover the full speed range with optimized performance. Electric motor drives employing digital-controlled power electronics systems can indeed improve overall performance than simple motors in their designed operating speed ranges. However, power electronics motor control systems are sophisticated and expensive to build.
For the foregoing reasons, there is a need for a power transmission apparatus that can transmit power within its full operating speed range with optimized performance characteristics.
The invention is directed to a power transmission apparatus for transmitting power at optimized efficiencies within the full operating speed range. A power transmission apparatus having features of the invention comprises a power-transmitting means and a power transmission interaction redistributing means. The power-transmitting means comprises a first transmission interaction element and a second transmission interaction element and is connected to the input of the apparatus for receiving an external power at an input angular speed. The first and the second transmission interaction elements operate at a first and a second angular speed respectively for transmitting power via interaction between the two. The transmission interaction redistributing means is integrated with the power-transmitting means and the output of the apparatus. The power-transmitting interaction of the power-transmitting means operating at the first and the second angular speeds is redistributed onto the output by the transmission interaction redistributing means, and the output delivers the power to an external load at an output angular speed.
In a mechanical implementation of the invention, a power transmission apparatus having features of the invention comprises a power-transmitting means and an epicyclic gear train. The power-transmitting means comprises a driving element and a driven element and is connected to the input shaft of the apparatus for receiving an external mechanical power at an input angular speed. The driving and the driven elements of the power-transmitting means operate at a driving and a driven angular speed respectively for transmitting the mechanical power via interaction between the driving and the driven elements. The epicyclic gear train comprises a first, a second and a third gear, the second gear rotates in the same rotational direction as the third gear and at an angular speed slower than the third gear when the third gear is driven while the first gear is held stationary. The third gear is connected to the driving element of the power-transmitting means, the second gear is connected to the driven element of the power-transmitting means, and the first gear is connected to the output shaft of the apparatus. The power-transmitting interaction of the power-transmitting means operating at the driving and the driven angular speeds is redistributed onto the output shaft of the apparatus by the epicyclic gear train, and the output shaft delivers the mechanical power to the external load at an output angular speed.
In an electromagnetic implementation of the invention, a power transmission apparatus having features of the invention comprises an electromagnetic power-transmitting means and a rotary commutator. The electromagnetic power-transmitting means comprises a first electromagnetic element and a second electromagnetic element. The electromagnetic power-transmitting means receives the external power at an input angular speed, and the first and second electromagnetic elements operate at a first and a second angular speed respectively for transmitting power via electromagnetic interaction between the magnetic fields established by the first and second electromagnetic elements respectively. The rotary commutator magnetizes the first electromagnetic element and is integrated with the first and second electromagnetic elements of the electromagnetic power-transmitting means. The rotary commutator operates at a commutation angular speed to magnetize the first electromagnetic element and establishes in the first electromagnetic element a first rotating magnetic field rotating at an angular speed that is synchronous with the angular speed of a second rotating magnetic field established by the second electromagnetic element. The power-transmitting electromagnetic interaction of the electromagnetic power-transmitting means operating at the synchronized angular speed of the first and second rotating magnetic fields is redistributed onto the output of the apparatus by the rotary commutator, and the output delivers the power from the electromagnetic power-transmitting means to the external load at an output angular speed.